I have sold on ebay since 1999. I only just started using their shipping labels about 2 years ago. It is cheaper. It is a negotiated rate so only ebay sellers can use it. I mostly sell small lightweight items. Otherwise I use facebook marketplace.
That's pretty much what I thought it must be...
If you had a 3 oz. item over 1" thick, it is then still a "package", right?
Unfortunately(?), I don't "do" Facebook.